I've had this happen before also. I figured that it took my average earnings and figured google was saying "eh, i'm sure you'll make at least 1 penny in the next thousand impressions" lol
Page impressions Clicks Page CTR Page eCPM [?] Earnings AdSense for Content 41 0 0.00% $0.00 $0.00 your lucky!
I make that quiet often and more. I am not sure if its against TOS so I will not list the exact price.
well when I image ads i always choose to pay per 1000 impressions instead of by click with adwords so it's only fair that adsense pay you.